Guru Puja on Janmashtami is an important puja to observe. Though, Sri Krishna is known as the Jagadguru, the Lord was very much obedient to his Guru, Sandeepani Muni. Hence, Guru Puja is considered very important to be performed on Sri Krishna Jayanti Pujan.
Guru Puja Mantras for Janmashtami Puja
Oṁ ajñāna-timirāndhasya jñānāñjana-śalākayā
cakṣur unmīlitaṁ yena tasmai śrī-gurave namaḥ
Nama oṁ viṣṇu-pādāya kṛṣṇa-preṣṭāya bhū-tale
śrīmate bhaktivedānta-svāmin iti nāmine
Namas te sārasvate deve gaura-vāṇī-pracārine
Hare kṛṣṇa hare kṛṣṇa kṛṣṇa kṛṣṇa hare hare
hare rāma hare rāma rāma rāma hare hare
Check this video for detailed Janmashtami Puja Procedure with Mantras and fully explained Puja steps..